Electric discharge tube comprising a mesh grid

ABSTRACT

In mesh grids of comparatively large dimensions, measures are taken to prevent that said grids which are mainly used in metalceramic tubes deform under the influence of their own weight at high temperature. A sufficient increase of the mechanical stability of the grid is obtained if said grid comprises a few thicker wires in addition to the thin wires.

United States Patent Hink'el 41 ELECTRIC DISCHARGE TUBE COMPRISING A MESH GRID Karl Walter Hinkel, Emmasingel, Eindhoven, Netherlands [75] Inventor:

73 Assignee: U.S. Philips Corporation, New

York, NY.

22 Filed: Feb. 2, 1973 21 App]. No.: 329,235

[30] Foreign Application Priority Data Feb. 5, 1972 Netherlands 7201534 52 U.S.Cl. ..313/34s,313/352 [51] lnt.C|. ..H01j1/46,H01j17/12,I-I01j1/52,

HOlj 19/38, HOlj 17/04, HOlj 19/40 [58] Field of Search 313/348, 352

[56] References Cited UNITED STATES PATENTS 2,882,436 4/1959 Dorgelo 313/348 X Apr. 23, 1974 3/1965 Johnson et a1 313/348 X 3/1942 Ronci 313/348 Primary Examiner-Archie R. Borchelt Assistant Examiner-Saxfield Chatmon, Jr. Attorney, Agent, or FirmFrank A. Trifari [5 7] ABSTRACT In mesh grids of comparatively large dimensions, measures are taken to prevent that said grids which are mainly used in metal-ceramic tubes deform under the influence of their own weight at high temperature. A sufficient increase of the mechanical stability of the grid is obtained if said grid comprises a few thicker wires in addition to the thin wires.

3 Claims, 1 Drawing Figure ELECTRIC DISCHARGE TUBE COMPRISING A MESH GRID The invention relates to an electric discharge tube comprising one or more cylindrical grids which are constructed from wires of molybdenum or a different metal having a high melting point, which wires are wound according to left and according to right helical lines and extend on either side along a same cylinder surface and welded together at the intersections.

Such a grid is known by the name of mesh grid and in known from the US. Pat. No. 2.795.726. Grids construct'ed in this manner which are often used as control electrodes in tubes having a high output power, maintain in general a sufficient mechanical stability in normal operating conditions. However, the temperatures to which the grid is subjected during operation of the tube are not an absolute measure of the required mechanical stability of the grid. The grid must also capable of withstanding extremely high temperatures during the manufacture. It is known, for example, from German Patent Specification 1,051,991 to check the thermal electron emission of such a grid occurring at high temperature by covering the wires of the grid with a thin layer of zirconium carbide which itself is covered again with a thin layer of platinum or gold. The zirconium carbide is provided on the grid wires in a furnace and under a neutral atmosphere by sintering at a temperature of approximately 2000C. It has been found,

however, that in mesh grids of large dimensions the mechanical rigidity at said high temperature has reduced to such an extent that the grid is inadmissibly deformed under the influence of gravity.

When the entire mesh grid is constructed from thicker wires, this results in an improvement of the mechanical properties of the grid, but said improvement is again nullified by the inadmissible increase of the grid current occurring as a result of the thicker wires.

It is an object of the invention to provide a mesh grid of the type mentioned in the preamble which can withstand a temperature treatment of at least 2000C without an inadmissible deformation occurring.

For that purpose, the mesh grid according to the invention comprises in addition to the thin wires of approximately the same cross-section a few thicker wires which are incorporated in the grid according to the same pattern and which, as regards position, are regularly distributed on the circumference of the grid.

It is to be noted that a mechanically reinforced grid is known per se from British Patent Specification No. 838,017. This specification, however, does not relate to a mesh grid, but to a grid which obtains its mechanical stability from a frame built-up from thick wires around which the actual thin grid wire is wound with a small pitch.

The mechanically reinforced grid is furthermore known from German Patent Specification No. 1,108,814. This specification also relates to a wirewound grid. Some of the supporting wires which in this case are equally thick or even thinner than the original grid wire are added to the grid longitudinally and others according to turns having a larger pitch than that of the grid wire, so as to shift the resonant frequency of the grid to higher frequencies.

In the grid according to the invention, the reinforcement wires are provided according to the same pattern as the grid wires. The original grid pattern is not disturbed, while in addition a particularly effective reinforcement of the grid is obtained. The contribution of the reinforcement wires to the rigidity of the grid is optimum if both the grid wires and the reinforcement wires enclose an angle of substantially 45 with the longitudinal axis of the grid.

In order to obtain a certain mechanical stability it will of course be necessary to choose the diameter of the thicker wires occurring in the grid according to the invention to be larger than would be necessary in the case in which all the wires of the grids would show a larger diameter so as to obtain the same mechanical stability. It has nevertheless been found that in the grid according to the invention the electrical properties of the tube are not or hardly influenced, while the grid maintains a sufficient mechanical stability up to a temperature of approximately 2000C.

The invention is used in particular in mesh grids having an axial length of more than 200 mm. Dependent upon the length and the diameter of the mesh grid according to the invention the diameter of the thick wires is from one-and-a-half to three times the diameter of the thin wires, the number of thick wires being from five to fifteen times smaller than the number of thin wires.

The invention will be described in greater detail with reference to the drawing which shows a grid according to the invention.

The grid comprises, for example 46 wires I wound according to left helical lines and, for example, 46 wires 2 wound according to right helical lines. The length of the grid is, e.g., 276 mm, the diameter is, e.g.,

I 83 mm and the pitch at which the molybdenum wires are wound is, e.g., 261 mm. At the intersections, for example at 3, the wires are welded together.

In order to improve the mechanical stabiity, the grid comprises, in addition to wires 1 having a diameter of, e.g., 0.325 mm, a few wires 4 which have a diameter of, e.g., 0.6 mm and likewise consist of molybdenum. In the present example, the arrangement of said thick wires 4 is such that between two successive thick wires 4 wound in the same sense alternatively, 10 or 1] thin wires, for example, are present.

What is claimed is:

1. An electric discharge tube including at least one cylindrical grid, said grid comprising first and second sets of wire elements of high melting point metal, said wire elements of said first and second sets extending along substantially the same cylindrical surface and forming respectively left and right helices, said wire elements being welded together at their intersecting places, said first and second sets individually comprising both relatively thin said wire elements and relatively thick said wire elements interspersed among said relatively thin wire elements.

2. An electric discharge tube as claimed in claim 1, wherein said relatively thin and said relatively thick wire element are disposed so asto form an angle of substantially 45 with the longitudinal axis of said grid.

3. An electric discharge tube as claimed in claim 1, wherein the diameter of said relatively thick wire elements is from one-and-a-half to three times that of said thin wires and the number of said relatively thin wire elements being from five to fifteen times larger than the number of said relatively thick wire elements. 

1. An electric discharge tube including at least one cylindrical grid, said grid comprising first and second sets of wire elements of high melting point metal, said wire elements of said first and second sets extending along substantially the same cylindrical surface and forming respectively left and right helices, said wire elements being welded together at their intersecting places, said first and second sets individually comprising both relatively thin said wire elements and relatively thick said wire elements interspersed among said relatively thin wire elements.
 2. An electric discharge tube as claimed in claim 1, wherein said relatively thin and said relatively thick wire element are disposed so as to form an angle of substantially 45* with the longitudinal axis of said grid.
 3. An electric discharge tube as claimed in claim 1, wherein the diameter of said relatively thick wire elements is from one-and-a-half to three times that of said thin wires and the number of said relatively thin wire elements being from five to fifteen times larger than the number of said relatively thick wire elements. 